1. Field of the Invention
The invention concerns an antenna, and is particularly directed to a disc-shaped slot antenna which is arranged transversely with respect to the longitudinal axis and concentrically in an artillery fuse.
2. Discussion of the Prior Art
An antenna of that kind is known for receiving satellite navigation information from U.S. Pat. No. 6,098,547 A in the structural form of a dielectric disc which is held transversely with respect to the axis of the system in the front region of an artillery fuse and which is metallically coated on both sides and which, for inductive adjustment of its resonance frequency, is provided with electrically conductive through passages, in parallel relationship with the axis, between the two metallisations. The adjustment options afforded by virtue of that arrangement however are really limited and are difficult to implement in terms of the practical demands. In particular however that antenna structure, either in itself or in terms of the apparatus integration options, does not have the desirable mechanical stability in relation to the acceleration forces which occur upon the launch of a spin-stabilised item of ammunition.
That applies in a corresponding manner to the axial stack, known from U.S. Pat. No. 4,305,078 A, of dielectric discs which are separated from each other by metallisation coatings, for forming a multi-frequency slot antenna through which axially passes the inner conductor of a coaxial antenna cable to a position for connection to the uppermost metallisation, with the outer conductor being connected to the oppositely disposed outer metallisation of the layer structure.
WO 99/02936 A2 discloses a droppable bomb which is provided at the centre of its tail with a sandwich-like or patch-like satellite antenna. During the dropping movement into the target area, the spherical characteristic thereof maintains contact with navigational satellites which are above the horizon in order to increase the hit accuracy by final phase control.
Such an antenna configuration is however inappropriate for artillery ammunition. For, the antenna directional characteristic which is oriented rearwardly from the tail antenna approximately symmetrically with respect to the longitudinal axis of the projectile would be directed, during the major part of the flight of an item of artillery ammunition along a more or less extended ballistic trajectory, only to the horizon, initially even therebelow and, after the apogee, only slightly thereabove. As a result, there would be a low level of probability of being able to simultaneously detect in a sufficiently trouble-free manner a number of navigational satellites, which would be sufficient for rapidly and precisely determining the point on the trajectory, for trajectory correction purposes. The installation of such a patch antenna in the tip of the projectile would also be unsatisfactory because its spherical characteristic which is then oriented coaxially forwardly would be directed markedly above the horizon only in the very first phase of the trajectory, but this is necessary in order to have contact with a plurality of satellites in a favourable configuration. After passing through the apogee the tip of an article of ammunition is then directed towards the ground again so that now at best it would be possible to pick up the very interference-afflicted ground reflections of satellite signals.
In addition, especially in the case of artillery ammunition, in view of the antenna characteristics which in practice are not ideally spherical in terms of axis symmetry, there is the problem of rotation for the purposes of spin stabilisation of ballistically launched projectiles or also only for the purposes of compensating for launch disturbances in the case of propulsion unit-accelerated and aerodynamically stabilised projectiles. For, the consequence of the antenna characteristic which is not circular in cross-section is that the signals are modulated in dependence on the rotational movement, and that severely adversely affects evaluation of the items of information which are thus communicated and therefore gives rise to a considerable increase in expenditure in terms of signal processing procedures.
Such rotationally-induced problems certainly occur when, in accordance with DE 44 01 315 A1, an unguided rocket, for GPS-aided trajectory correction by transverse thrust which if necessary is to be triggered in dependence on direction in space, is provided with a plurality of propulsion units which are strapped to the outside peripheral surface of the rocket body by clamping bands, in which respect at least one of those propulsion units is additionally equipped with a GPS antenna which is not described in greater detail therein. A trouble-free panoramic characteristic is not something to be expected from such an asymmetrical clamping band antenna configuration.
Comparable problems arise if, by means of the antenna, it is not items of information from satellites (such as items of positional information from navigational satellites) that are to be picked up and processed on board the ammunition, but rather if items of information are to be communicated from the ammunition by means of telemetry senders to geostationary or orbital receiving or relay stations.